Flame detector



y 2, 1956 F. T. DEZIEL ETAL 2,747,112

FLAME DETECTOR Filed Feb. 25, 1955 R 1 LONG DROP oufi 68 e2 :IGN.: 74TIME RELAY 52 95 IO N 85 L V 6 l4 J l g INVENTORS FRED T. DEZIEL HARVEYJ. SMITH ATTORNEY 8 Claims. (M. 367-432) The present invention isconcerned with a flame detector and more particularly with an electronictype flame detector utilizing means for checking the proper operation ofthe flame detector.

Electronic flame detectors have found wide acceptance in both domesticand commercial use. They are of particular utility in the case of largecommercial fuel burners which discharge a large quantity of fuel intothe fire box per unit time. The electronic flame detector has thecharacteristic of detecting the presence or absence of flame in a veryshort time and therefore in the case of a flame failure the supply offuel to the fire box is cut off before a dangerous amount of fuel ispumped into the fire box.

However, as with all electronic devices, the device is subject tomalfunction in the case of a failure of one or more of the variouscomponents of the device. In the case of an electronic flame detectorthese failures can be either of a safe or of an unsafe nature.

A safe failure is the type of failure wherein the electronic flamedetector fails in a condition to indicate that there is no flame presentwhen in fact a flame may actually be present at the burner. Thisfailure, while being undesirable, would have the effect of turning offthe supply of fuel and therefore it is called a safe failure.

An unsafe failure is that type of failure wherein the flame detectorcontinues to indicate a flame at the fuel burner independent of whetheror not a flame exists at the burner. in this type of failure, fuel iscontinuously supplied to the tire box and if the flame is extinguishedan explosion may occur on reignition. For this reason it is called anunsafe failure.

Prior electronic burner controls have utilized what is called acomponent checking arrangement wherein the ability of the electronicflame detector to operate properly is checked during the standbycondition of the burner. That is, the prior electronic burner controlsprovided means whereby a safety switch would be actuated if at the endof a call for operation of the fuel burner the flame detector did notindicate that the flame had been extinguished at the fuel burner.However, once there is a call for heat and a flame is established at theburner the flame detector continuously indicates the presence of flameand it is possible for an unsafe failure to occur at this time. if suchan unsafe failure did occur and if the flame then goes out the flamedetector would be unable to sense the absence of flame and an explosionmay occur on reignition.

it is an object of the present invention to provide an improved flamedetector wherein the flame detector is continuously checked during therunning period of the burner and this checking is facilitated by meansof an electrical feedback arrangement utilizing a gaseous discharge buibto control the voltage applied to an electrically operable flame sensor.

It is a further object of the present invention to provide an electronicflame detector utilizing an electrically 2,747,112 I Patented May 22,1956 lated absence of flame.

It is still a further object of the present invention to provide animproved flame detector having an electrically operable flame sensorcontrolling the conduction of a first electron discharge device, havinga second electron discharge device to control the operating voltage ofthe flame sensor to cause the flame sensor to be rendered insensitive toflame when the second discharge device is in a conducting state, andhaving an electrical feedback means including a gas tube connecting theoutput of the first discharge device to the input of the seconddischarge device to render the second discharge device conductive whenflame is detected by the flame sensor.

These and other objects of the present invention will be apparent tothose skilled in the art upon reference to the following specification,claims and drawings of which:

The single figure is a schematic representation of the presentinvention.

Referring to the single figure, the reference numeral 19 designates aburner unit having a main burner 11, a main burner valve 3.2, a pilotburner 13, and a pilot burner valve 14 Associated with the pilot burner13 is an ignition transformer 15 which is arranged to ignite the gasflowing from the pilot burner 13. The pilot burner 13 is associated withthe main burner 11 in a manner to ignite the gas flowing from the mainburner 11.

A photocell or electrically operable flame sensor 16 is positionedrelative to the burners ill and 13 to sense the flame present at theburners. Photocell 16 has been shown as the photoemissive type having ananode 74 and a cathode 73.

The reference numeral 17 designates a thermostat which is located in thespace to be heated by the burner unit ltl. Thermostat l7 closes anenergizing circuit for a relay 18 and a heater of safety cutout device91 upon a need for operation of the burner unit 10.

Safety cutout device 91 includes a heater 90, a bimetal element 92,normally closed switch 93, and manually operable reset button 94. Device91 functions such that after a predetermined time period of energizationof heater 9% the bimetal 92 warps to the right and causes switch 93 tobe opened. When bimetal 92 has cooled, switch 93 can be reset bydepressing button 94.

The relay 18 has a winding 19 which is energized from the secondary 20of a transformer 21 having a primary 22 connected directly to power lineconductors 23 and 24, which conductors are connected to a source ofalternating current voltage, not shown.

The relay 18 also includes a switch blade 25 and a stationary contact26. Relay 1? is shown in its deenergized position wherein the switchblade 25 is biased, by means, not shown, to disengaged contact 26. Uponenergization of relay 18 the switch blade 25 moves into engagement withcontact 26.

The reference numeral 27 designates a transformer having a primarywinding 28, which is connected to power line conductors 23 and 24, andhaving a secondary winding 29 and a secondary winding 30.

Secondary 29 is connected to an electrical network including electrondischarge devices 31 and 32. Discharge device 31 has an anode 33, acontrol electrode 34, a cathode 35, and a filament heater 36. Thedischarge device 32 has an anode 37, a control electrode 38, a cathode39, and a filament heater 40. The filament heaters 36 and eralconventional relays having this characteristic. example, relay may be ofthe type having a slugged ava ar in shown in the energized conditionwherein the switch blade 44 engages contact 55. Upon relay beingde-energized the switch blade 44 is biased, by means not shown, todisengage contact 45 and to move into engagement with contact 46.

' The reference numeral 47 designates a neon bulb, or gas tube, whichconnects the anode 33 of discharge device 31 to the control electrode 3%of discharge device 32. Switch blade and contacts 45 and of relay areconnected in a further electrical network which ineludes a directcurrent voltage source iltlli, a capacitor 48, acapacitor 49, and arelay 5d. Relay 5% is of the type having a long; dropout time and may beone of sev For core to provide for long dropout timing of the relay. The

relay '50 includes winding 5%, movable switch blades Hand 95, andstationary contacts 53 and 9d. The relay 50 is shown in thetie-energized condition wherein movable switch blades 5'2 and 95 arebiased, by means not .shown, to be out of engagement with contacts 53and )6 respectively. Upon energization of relay 5t switch blades 52 and95 move into engagement with stationary contacts 1'53 and 96.

The apparatus of the present invention is shown in the standbycondition. That is, the primary windings 22 and 28 of transformers 21and 2'7 are energized, the thermostat 17 is in the condition indicatingno need for operation of the burner unit lid, the relay 421 isenergized, the relay 5b is d'l'l6l'lZd, the relay 1% is de-energized,and there is no flame present at the burners 11 or 13.

With the apparatus in the standby condition the electron'dischargedevice 31 is in a conducting state and the E electron discharge device32 is substantially cut off.

This can be seen by tracing the current flow circuit for dischargedevice 33 from the right-hand terminal of secondary 29 through conductorse, winding 4-2, condoctor-'61, anode 33 and cathode 35, and conductor62 to the left-hand terminal of secondary 29. This current flow circuitcauses a voltage'ot the polarity indicated to exist across capacitor 43.

When the voltage across capacitor reaches a given value the-neon bulb4'7 tires to cause a capacitor 63 to be charged to the polarityindicated. This charging circuit can be traced from the upper terminalof capacitor 4.; 1 through conductor 69, conductor conductor 65, conasecondary 29 through a circuit which can be traced from the right-handterminal of secondary 29 through conductor 64, ground connection 67,ground connection es, photocell 16, conductor es, resistor 7t? shuntedby capacitor ll, resistor F2, and conductor 6?; to the left-handterminal of secondary 29. Current flows in this above traced circuitonly when the voltage of secondary Z9 is in the halfcycle wherein theanode '74 is positive with respect to the cathode 73 and then only whenflame is present at the burner 11 or 13. When current does flow in thiscircuit the capacitor 73 is charged to the polarity indicated andsubstantially cuts otf current flowing through the discharge device 3?.tothereby cause relay 41 to be deenergized.

Upon the thermostat 17 indicating a need for operaon of the burner uniti the energizing circuit for reater and for the windiu 2 .9 of relay 18is comleted causing switch blade to engage contact 26. s completes anenergizing circuit for the pilot valve and the ignition transformer Thiscircuit can 3 tr cedironr the. power line conductor. 24 through eludecontact conductor Bil, conductor 82,

- valve 14 connected in parallel with ignition transormer l5, andconductor 83 to the'power line conductor With the energization of pilotvalve 14, gas flows to the pilot burner 13 and is ignited by theignition transer The photocell 36 has an operative voltage i thereto atthis time and is subjected to the flame p se t at the pilot burner 13.Therefore, a current flows through the above traced circuit chargingcapacitor '71. This current is a pulsating current and flows on the halfcycle of the alternating current source during which the lefthandterminal of the secondary 2? is positive. After a few cycles of thealternating current source the capacitor fit is charged to'thcvoltageshown and causes the discharge device to be substantially cut oil.

With the discharge device 31 cut oil: the voltage which exists acrosscapacitor 23 leaks oil through the winding 4?. of relay 'After ashortperiod of time, relay 41 is tie-energized.

'At the same time that the voltage across capacitor is being reduced dueto the current flow through the winding-42 of relay 4%, the neon bulb 57is extinguished due to the fact that the voltage on capacitor 43 issubstantially reduced. The voltage on capacitor 63 can now leak oilthrough the resistor 66.

After a short period of time the charge on capacitor 63 is substantiallyreduced and the discharge device 32 is rendered conductive. Theconduction circuit for this discharge device can be traced from theleft-hand terminal of secondary 29 through conductor 62, resistor 72,conductor 34, anode 37, cathode 39, conductor 65,

and conductor 64 to the right-hand terminal of secondary 29.' From thiscircuit it-can be-seen that current flows through the discharge device32 during the same portion of the alternating current voltage cycle inwhich current flows through the photocell 16. I Namely, when thelefthand terminal of secondary 25 is positive, the current conducted bythe discharge device 32 is of a relatively high magnitude and causessubstantially all of the voltage of secondary 29 to-be dropped acrossthe resistor 72. This causes an appreciable reduction in the voltageapplied to the anode '74 and cathode -73 of photocell 16 and therebyrenders the photocell ltd-inoperative to sense the flame at the pilotburner i3.

'Therefore, a current no longer flows to charge the capacitor 71 andafter a short period of time the discharge device 31 is again renderedconductive to energize the winding 32 of relay 41.

The conduction of discharge device 31 again causes a voltage to appearacross capacitor 43 which has the effect of again rendering thedischarge device 32 nonconductive. This in turn once again causes anoperative voltage to be applied to the electrodes of the photocell l6and the photocell 16 is once again rendered operative to sense the flameat the pilot burner 13.

The above explanation has traced a single cycle of the apparatus whereinthe photocell l6 senses a flame to render the discharge device 31nonconductive, the voltage across capacitor id is dissipated to renderthe discharge device 32'conductive, the conduction of discharge device32 through resistor '72 renders the photocell 16 insensitive to thepresence of flame, the discharge device 31 is again rendered conductiveto charge capacitor 43 and the discharge device 32 is again renderednonconduc- '5 tive to once again render the photocell 16 sensitive tothe presence of flame.

From this it can be seen that relay winding 42 is cyclically energizedand then de-energized so long as the photocell continues to sense thepresence of flame when an operative voltage is applied thereto and togive an indication of the absence of flame when the voltage appliedthereto is of a magnitude to render the photocell 16 inoperative tosense the flame.

If any of the components associated with the discharge devices 31 or 32,or the discharge devices themselves, fail, the winding 42 of relay 41cannot be cyclically energized and will either be continuouslymaintained energized or continuously maintained de-energized. Forexample, if a cathode-to-anode short occurs in the discharge device 31the relay 41 will be maintained continuously energized. As a furtherexample, if the cathode 39 of discharge device 32 loses its electronemitting properties the relay =51 will be continuously energized in theabsence of flame and will be continuously de-energized in the presenceof flame.

Energization of relay 50 depends upon the cyclic energization of relay41 as will now be described. When relay 41 is in the energized conditionthe switch blade 44 is connected to contact 45 and capacitor 49 ischarged from the direct current voltage source 101. When relay 41 isde-energized the switch blade 44 engages contact 46 and transfers thecharged capacitor 49 to the winding 51 of relay 50. The capacitor 49therefore dissipates its charge causing a current to flow through thewinding 51 and causing relay 50 to be energized.

With relay 41 cycling, the capacitor 49 is alternately charged from thedirect current voltage source 101 and then discharged through thewinding 51. Since relay 50 has a long dropout timing the switch blades52 and 95 remain in contact with contacts 53 and 96 during the period oftime during which capacitor 49 is being charged from direct currentsource 101.

The explanation of the apparatus thus far has shown how a flame isestablished at the pilot burner 13 and how the photocell 16, inconjunction with the discharge devices 31 and 32 and the associatedcomponents, causes the relay 41 to cycle between the energized andde-energized positions and thereby causes the relay 50 to be energizedto cause switch blades 52 and 95 to engage contacts 53 and 96.

When switch blade 52 engages contact 53 an energizing circuit iscompleted for the main burner valve 12. This circuit can be traced frompower line conductor 24 through switch blade 25, stationary contact 26,conductor 86), contact 53, switch blade 52, conductor 85, main burnervalve 12, conductor 86, and conductor 83 to the power line conductor 23.With energization of the main burner valve 12 the gas flows to the mainburner 11 and is ignited.

When switch blade 95 engages contact 96 a circuit is completed to shuntheater 90 of cutout device 91 and thereby prevent switch 93 fromopening.

So long as there is a call for operation of the burner unit 10, by thethermostat 17, the relay 41 continues to cycle in response to the cyclicmanner in which the photocell 16 is first rendered operative and theninoperative to sense the presence of flame. So long as this cyclicaction of relay 41 continues the relay 50 will remain energized to causegas to be continuously supplied to the main burner 11. It can thereforebe seen that the present invention provides for a continuous checking ofthe operativeness of the flame detector by requiring the flame detectorto first sense the presence of the flame and then to sense a simulatedabsence of flame which is caused by applying a reduced voltage to theelectrodes of the photocell 16 to render the photocell 16 inoperative.

When the thermostat 17 is satisfied the relay 18 is deenergized to turnoff the valves 12 and 14 and the ignition transformer 15. The apparatusthen returns to the standby condition shown.

From the above description, it can be seen that an improved flamedetector has been provided wherein means is provided to check theoperability of the flame detector.

Modifications of the present invention will be ap parent to thoseskilled in the art and it is intended that the scope of the presentinvention be limited solely by the appended claims.

We claim as our invention:

1. A condition detector for detecting a given condition comprising: anelectrically operable condition sensor, a source of voltage, impedancemeans, means connecting said condition sensor and said impedance meansto said source of voltage to apply an operating voltage to saidcondition sensor, means controlled by said condition sensor, an electrondischarge device having an anode and cathode and a control electrode,means connecting said discharge device anode and cathode in series withsaid impedance means to said source of voltage to cause a voltage dropto exist across said impedance means when said discharge device isconductive to thereby control the magnitude of the condition sensoroperating voltage, and a gas tube connected from said means controlledby said condition sensor to said control electrode to render saiddischarge device nonconductive in the absence of the given condition.

2. Flame detector comprising: a source of voltage, a first electrondischarge device having an anode, a cathode and a control electrode, arelay having a winding and switch means, means connecting said firstdischarge device anode and cathode in series with said relay winding tosaid source of power to energize said winding when said first dischargedevice is conductive, an electrically operable flame sensor connected tosaid source of voltage and connected in controlling relation to saidfirst discharge device control electrode to cause said first dischargedevice to normally be conductive in the absence of flame andnonconductive in the presence of flame, means including a gas tubeconnected to said relay winding and connected to control the voltageapplied to said flame sensor to render said flame sensor inoperative tosense flame when the voltage across said relay winding is insuflicientto break down said gas tube to thereby cause said relay switch means tocycle when said flame sensor is subjected to a flame, and meansresponsive to continuous cycling of said relay switch means.

3. Flame detector comprising: a source of voltage, an electricallyoperable flame sensor, a voltage dropping impedance, means connectingsaid flame sensor and impedance in series to said source of voltage toapply an operating voltage to said flame sensor, a first controllableconducting device connected to said source of voltage, means connectingsaid flame sensor in controlling relationship to said first conductingdevice to cause said first conducting device to normally be conductivein the absence and nonconductive in the presence of flame, a furthercontrollable conducting device, means connecting said further conductingdevice in series with said impedance to said source of voltage to causesubstantially all of the voltage of said source of voltage to be droppedacross said impedance when said further conducting device is conductiveto thereby cause a low voltage to be applied to said flame sensor torender said flame sensor inoperative, circuit means connecting saidfirst conducting device in controlling relation to said furtherconducting device to render said further conducting device nonconductivein the absence of flame to thereby cause a high voltage to be applied tosaid flame sensor to render said flame sensor operative, and meansoperative in response to a cyclic state of conduction and nonconductionof said first conduction device.

4. A condition detector for detecting a given condition comprising: asource of voltage, an electrically operable condition sensor, voltagedropping impedance means, circuit means connecting said condition sensorin series with said impedance means to said source of voltage, acontrollable current conducting device, means connecting said conductingdevice in series with said impedance means to said source of voltage,said conducting device when conducting causing a voltage drop acrosssaid impedance means to render said condition sensor inoperative tosense the given condition, means controlled by said condition sensor andeffective to cause said conducting device to conduct current only whensaid condition sensor is subjected to the given condition, and meansresponsive to and operative upon cyclic periods of said condition sensorsensing the given condition followed by a period of said conditionsensor sensing a simulated absence of the given condition due to saidcondition sensor being rendered inoperative.

5. A flame detector comprising: a source of alternating current voltagehaving a first and a second terminal, a relay having a winding andswitch means, a first electron discharge device having an anode, acathode and a control electrode, means connecting said first dischargedevice cathode to the first terminal of said source of voltage; meansconnecting said first discharge device anode through said relay Windingto the second terminal of said source of voltage; an electrical flamesensor, voltage dropping impedance means, means connecting said flamesensor to said source of voltage through said impedance means, meansconnecting said flame sensor in controlling relation to the firstdischarge device control electrode to render said first discharge devicenonconductive when said flame sensor both has an operative voltageapplied thereto and is subjected to a flame; a second electron dischargedevice having an anode, a cathode and a control electrode, meansconnecting said second discharge device cathode to the second terminalof said source of voltage, means connecting said second discharge deviceanode to the first terminal of said source of voltage through saidimpedance means, voltage responsive means connected to said relayWinding and to said second discharge device control electrode andeffective to cause said second discharge device to be conductive whensaid first dischar e device is nonconductive to thereby cause a voltagedrop across said impedance means to cause an inoperative voltage to beapplied to said flame sensor; and means responsive to continuous cyclingof said relay switch means.

6. A flame detector comprising: a source of alternating current voltagehaving a first and a second terminal, a relay having a winding andswitch means, a first electron discharge device having an anode, acathode and a control electrode, means connecting said first dischargedevice cathode to the first terminal of said source of voltage; meansconnecting said first discharge device anode through said relay Windingto the second terminal of said source of voltage; an electrical flamesensor, voltage dropping impedance means, means connecting said flamesensor to said source of voltage through said impedance means, meansconnecting said flame sensor in controlling relation to the firstdischarge device control electrode to render said first discharge devicenonconductive when said flame sensor both has an operative voltageapplied thereto and is subjected to flame; a second electron dischargedevice having an anode, a cathode and a control electrode, meansconnecting said second discharge device cathode to the second terminalof said source of voltage, means connecting said second discharge deviceanode to the first terminal of said source of voltage through saidimpedance means, voltage responsive means connected to said relayWinding and to said second discharge device control electrode andellieclive to cause said second discharge device to be conductive whensaid first discharge device is nonconductive to thereby cause a voltagedrop across said impedance means to cause an inoperative voltage to beapplied to said flame sensor; a source of direct current voltage, acapacitor, a long dropout time relay having an actuator, and circuitmeans controlled by said relay switch means to cyclically connect saidcapacitor to said source of direct current voltage and then connect saidcapacitor to the actuator of said long dropout time relay in response tocycling of said relay switch means.

7. A condition detector comprising: a first electron discharge devicehaving an input and an output, an electrically operable conditionsensor, means connecting said condition sensor to the input of saidfirst discharge device in a manner to control the conduction of saidfirst dis charge device, a second electron discharge device having aninput and an output, means connecting the output of said first dischargedevice to the input of said second discharge device to control theconduction of said second discharge device, and means including theoutput of said second discharge device to control the operativeness ofsaid condition sensor to render said condition sensor cyclicallyoperative and then inoperative upon said condition sensor beingsubjected to a condition to be detected.

8. A flame. detector comprising: a first electron discharge devicehaving an input and an output, an electrically operable flame sensor,means connecting said flame sensor to the input of said first dischargedevice in a manner to control the conduction of said first dischargedevice, a second electron discharge device having an in ut and anoutput, means connecting the output of said first discharge device tothe input of said second discharge device to control the conduction ofsaid second discharge device, means including the output of said seconddischarge device to control the operativeness of said flame sensor torender said flame sensor cyclically operative and then inoperative uponsaid flame sensor being subjected to a flame, and means responsive toand operative upon said flame sensor cyclically sensing flame whenoperative and then sensing the absence of flame when inoperative.

No references cited.

